As human bacterial infections have become more manageable and treatable through the use of increasingly available antibiotic agents, viral infections have remained a more difficult and less treatable target. Emphasis in finding agents to treat viral infections has remained a high priority.
Epstein-Barr virus (EBV is an important human pathogen, related to herpes simplex virus (HSV). Elliot Kieff, Virology Third Edition, Edited by B. N. Fields, D. M. Knipe, P. M. Howley, et al. Epstein-Barr Virus and Its Replication. Chapter 74. Pp 2343-2396 and Alan B. Rickinson and Elliot Kieff, Ibid. Chapter 75, pp. 2397-2446. EBV is a lymphotrophic member of the genus Lumphocryptovirus, and belongs to the sub-family gammaherpesvirinae. Another new member of human virus also belonging to this family is Kaposi's sarcoma-associated herpes virus (KSHV/HHV8). Chang, et al., Science, 266:1865-1869 (1994); Cesarman, et al., N. Eng. J. Med., 332:1186-1191 (1995); Soulier, et al., Blood, 86:1276-1280 (1995). There are two subtypes of EBV identified and their genomes are nearly identical, but there is no clear relationship between EBV associated diseases and EBV sub-types. Abdul-Hamid, et al., Virology, 190: 168-175 (1992) and Sample, et al., J. Virol. 64:4084-4092 (1990). The lytic EBV genome is a linear, double-stranded, 172 Kbp DNA composed of 60 mol % guanine and cytosine. The genome has been sequenced and it was found to be capable of encoding a number of virus specified proteins, which include several enzymes involved in virus DNA synthesis during lytic infection of EBV. In vitro, EBV infection is generally limited to B-lymphocytes, although epithelial cells can also be infected. Sixbey, et al., Nature, 306:480-483 (1983). In humans, the virus genome can be detected in B-lymphocytes and T-lymphocytes as well as epithelial cells. The EBV genome replicates lytically in the linear form and can also be latent as supercoiled circular DNA. The expression of the EBV genome in lytic infected cells is very different from latent infected cells. EBV specified DNA plymerase, Dnase and dTbd kinase are only expressed in cells upon lytic DNA replication. Cell culture studies indicated the essential role of EBV specified DNA polymerase for EBV DNA replication during lytic infection, but not for the maintenance of supercoiled EBV DNA in latent infected cells. A unique set of EBV proteins including EBVNA 1 and sometimes, EBNA LP, 2, 3A, 3B, 3C, LMP1 as well as LMP2 is expressed in latent infected or transformed cells. Elliot Kieff, Virology, Third Edition, Edited by B. N. Fields, D. M. Knipe, P. M. Howley, et al. Epstein-Barr Virus and Its Replication. Chapter 74. Pp 2343-2396 and Alan B. Rickinson and Elliot Kieff, Ibid. Chapter 75, pp. H2397-2446.
Structurally, EBV is similar to that of other herpes viruses--it has a double-stranded DNA genome contained within a nucleocapsid, which is surrounded by a lipid envelope containing viral glycoproteins. A tegument protein occupies the space between the envelope and the gucleocapsid.
While primary EBV infection in infancy appears to be almost asymptomatic, a proportion (in some studies up to 50%) of serologically confirmed primary infections in adolescence or early adult life are manifested as infectious mononucleosis (IM) also called the "Kissing Disease". Transmission of EBV is primarily through the saliva, although some infections are transmitted via blood transfusions. A high percentage (&gt;85%) of patients in the acute phase of infectious mononucleosis secrete EBV. In the mid-1970's, EBV was identified to cause fatal IM/X-linked lymphoproliferative syndrome (XLP) in young male children who had X-linked immunodeficiency. Sullivan and Wood, (Immunodeficiency Rev. 1:325-347 (1989). Fatal EBV infection is also found to be associated with nonfamilial monophagocytic syndrome (VAHS) for which there is no effective therapy. Alan B. Rickinson and Elliot Kieff, Virology, Third Edition, Edited by B. N. Fields, D. M. Knipe, P. M. Howley, et al. Epstein-Barr Virus and Its Replication, Chapter 75, pp. 2397-2446 and Craig, et al., Am. J. Clin. Path., 97:189-194 (1992).
Epstein-Barr virus is also recognized as a causative agent of B-cell proliferative diseases, and is linked to a variety of disease states, including a rare progressive mononucleosis-like syndrome and oral hair leukoplakia in AIDS patients. EBV has also been associated with certain types of cancer such as Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease, EBV-associated T-cell lymphoma and nasal T-cell lymphoma. Certain patients, in particular, those with suppressed immune systems such as AIDS patients and organ transplant patients who are being treated with immunosuppressive agents, are particularly susceptible to EBV manifestations, especially the development of EBV-associated lymphomas.
Chu, et al., in PCT application PCT/US95/01253, describe a number of L-nucleoside analogs for use in the treatment of Hepatitis B virus and Epstein-Barr virus infections. One agent disclosed in the PCT application, 2'-fluoro-5-methyl-.beta.-L-arabinofuranosyluridine (L-FMAU), showed good activity against EBV. Noteworthy is the fact that when a 5-methyl group of L-FMAU was substituted with a bromo group, the anti-EBV activity decreased.
Several compounds have been shown to have activity against EBV replication in culture at concentrations non-toxic to cell growth. These include acyclovir (ACV), gancyclovir (DHPG), pencyclovir, D-FMAU and its analogs, 5-bromovinyl dUrd, phosphonoformate and phosphorothioate oligonucleotides. See Lin, et al., Antimicrob. Agents and Chemo. (February) 32(2):265-267 (1988); Lin, et al., Antimicrob. Agents and Chemo., 32(7):1068-1072 (1988); Cheng, et al., Proc. Natl., Acad. Sci. USA, 80:2767-2770(1983); Datta, et al., Proc. Natl., Acad. Sci. USA, 77:5163-5166 (1980); Datta, et al., Virology, 114:52-59 (1981); Lin, et al., Antimicrob. Agents and Chemo., 31:1431-1433 (1987); Olka and Calendar, Virology 104:219-223 (1980); Lin, et al., J. Virol., 50:50-55 (1984); Yao, et al., Antimicrob. Agents and Chemo. 37:1420-1425 (1993) and Yao, et al., Biochem. Pharm., (51):941-947(1966).